Tape reels commonly comprise a hub which is cylindrical in form and which extends between a pair of flanges, one at each end. The hub has a length only a little longer than the width of the tape that it is to accommodate. In practice, the diameter of the flanges is often twice as great, or more, than the diameter of the hub, and the difference in diameters usually exceeds the distance between the two flanges three or four times, or more. The effect of those dimensional relationships is that it is difficult, or even impossible, for a user of tape reels to reach down into the space between the flanges to the hub. That has made it difficult to secure the tape to the reel in a manner that will prevent relative movement between tape and the hub until a few turns of the tape have been wound upon the hub.
In general, if relative motion between the end of the tape and the hub can be prevented until several turns of the tape have been wound upon the hub, the pressure of subsequent turns of tape is sufficient to insure frictional engagement between the hub and the tape so that slippage is prevented. However, magnetic tapes and films are usually made of materials whose surfaces exhibit a low coefficient of friction, and to start the winding has been a continuing and serious problem. One inexpensive solution has been to form the hub with slots that extend over the length of the hub and are accessible from the ends of the reel through openings formed in the flanges. That arrangement works and is commonly employed in inexpensive reels. However, it is not a satisfactory solution, because, in most instances, the tape must be held manually in that slot while the reel is rotated several times, usually with the other hand.
There are certain cases in which it is possible to fix a stop structure on the end of the tape and to insert that into a stop-receiving opening in the hub. That solution is not available if the tape must be free to run off the reel as an insurance against damage of the tape, or otherwise. In practice, most applications preclude the use of a stop or other positive fastening element.
An alternative to placing the end of the tape loosely in a slot is to hold the tape in a clamp which operates by frictionally engaging the tape with a pressure insufficient to prevent the tape from pulling free, but which exerts enough frictional force to permit commencement of the winding without manual operation beyond the original clamping action. A variety of complex clamping structures have been proposed. The art of plastic forming is sufficiently advanced so that complexity alone is not a deterrent to successful operation. However, complexity has brought dissymmetry. Structural arrangements that move the center of gravity of the unit away from its geometrical center, and which tend to increase the moment arm of inertia, are not satisfactory for incorporation in reels that are to be used in those cases where the angular momentus of the reel and the system "WOW" must be held to a minimum.
One of the major difficulties with prior designs is that they fail to insure that the hub surface is truly cylindrical once the tape is clamped in place. Out-of-round conditions are magnified as more and more tape is wound upon the reel. As the reel is filled, out-of-roundness in the stored tape results in ever increasing displacement of the centroid from the rotational axis of the reel. The ultimate result is loss of fidelity and a reduction in usefulness of such reels for music reproduction and for high-speed data storage and recovery applications.
Another difficulty with prior designs is that they require weak flanges with radial splits or large openings which expose the tape edges.
The major problem with prior designs is that they are difficult, slow, uncertain, and cumbersome to attach a tape to in preparing for winding.